Individual cells can be manipulated by tiny vortices generated in fluids, rather than by the potentially harmful lasers or electric fields typically used. The concept is the brainchild of Li Zhang and his colleagues at the Swiss Federal Institute of Technology in Zurich, who used the vortices to control the movement of microscopic objects.
The team placed a tank of water in a rotating magnetic field, which triggered nickel nanowires in the tank to rotate in turn, generating microvortices. The vortices trapped polystyrene microbeads in the water. By controlling the movement of the nanowires, the authors could tightly control the movement of the beads.
They also successfully manipulated Escherichia coli bacteria using a pair of microspheres in place of the nanowires.